Aquaculture food production grows faster than other major food production sectors, and in the Faroe Islands, salmon accounts for nearly half of the countries export value. In order to to keep up width the global trend, fish-farming in the Faroe Islands has moved from sheltered locations, to more exposed farming sites. Understanding the behaviour of fish-farming equipment and their inhabitants at exposed sites is important for ensuring fish welfare, and by extension, profits. Measurement equipment and methods make used today make it difficult to obtain an accurate description of the spatial extent and dynamics of the cage and the fish distribution and movement within, since the cages are very large and in exposed sites are subject to large deflections and deformations. Sonars have a comparatively high range, compared to optical cameras, but lack the ability to measure in different direction. Multibeam sonars allow for spatial information of its surroundings to be gathered, both in the spatial and temporal domain.
In this study we investigate imaging a fish-cage with a iXblue Seapix 3D multibeam sonar. The sonar is suspended 2 meters from the water surface, and 2 meters from the side net of a fish-farm. The preliminary results show that the extent of the cage can be determined, and within the first 10m, individual fish can be seen.
Since we have verified the information of cage extent and fish distribution can be found using this method, the next step is to develop a cage detection method that utilizes nearby angles as well as multiple pings. Combining these will result in a 3d model of the cage, from witch, the volume can be calculated.